[porky69]

It all depends on the unit and how it is used and/or maintained. But short answer is no the medium duty engines generally do not last like the HDT engines do. Most are underpowered for what most people expect of them(which is more than they are designed to do) and as a result they get abused.

If I were to have to choose from your choices I would get a diesel with the most complete, up to date, best looking service records...which any leasing or rental company should have available for any unit they are selling.

Personally I would be tempted to buy a long wheelbase highway tractor and buy a used box off of a UHaul/Penske and mate the two, you will be a lot happier with the performance and durability... but that is just me, after looking at factory built truck conversions on both MDT and HDT chassis. If I hadn't found the Haulmark I bought I was going to buy a Pete 379 and have a local truck body builder build me a box with slides and do the interior myself.